The document discusses modals of deduction in English, which are used to express degrees of certainty about situations. It explains that must is used when something is considered very likely due to strong evidence, while might, may, and could indicate something is possible but not certain. Can't expresses certainty that something is not true. Examples are provided for each modal. The document also discusses using these modals to make deductions about past events, and provides practice questions for readers to fill in modals of deduction.